Krill evolution and the Antarctic ocean currents: Evidence of vicariant speciation as inferred by molecular data

The phylogenetic relationships of the Antarctic krill Euphausia superba, the key species in the Antarctic food web, and other Antarctic and sub-Antarctic euphausiids have been investigated using the 16S ribosomal mitochondrial gene. The phylogenetic reconstructions indicated that the Antarctic species form a monophyletic clade separated by the non-Antarctic species. The results revealed a large genetic divergence between the Antarctic (E. superba and E. crystallorophias) and sub-Antarctic species (E. vallentini). The time of separation between these species, estimated from the molecular data, is around 20 million years ago, which is comparable with the geological time of the formation of a circum-Antarctic water circulation and the Antarctic Polar Frontal Zone. The euphausiid molecular phylogeny therefore represents evidence for vicariant speciation.